This invention relates to a mining method and more particularly to a method for the electrical sequential initiation of explosions in mines.
The accurate sequencing of explosions in underground mining operations is of the utmost importance. In advancing a tunnel or stope, sequential blasting is used to ensure that rock is moved in the requried direction and to achieve efficient "chiselling" of the rock mass. Both out-of-sequence blasts and misfires can accordingly have significant adverse effects on mining production.
In concentrated reef mining, blast holes are drilled at spaced positions along the stope face. The holes are often staggered, with the upper ones inclined upwardly and the lower ones inclined downwardly. Each hole is charged with an explosive charge surrounding a detonator. Up to now it has been proposed to use a delay element associated with each detonator. The delay element can be a fuse which burns in the hole or it can be provided in the detonator itself, in which case it can function electronically or chemically.
Initiating means are used to initiate the series of delay elements according to the sequence of explosions required. If all the delay elements are initiated before the first explosion occurs, the initiating means are not disrupted or cut off. However, in some cases initiation can still be in progress when the first explosion occurs.
One of the most important factors in the provision of means for the control of sequenced explosions in mining operations, is cost. The most inexpensive initiating system is the pyrotechnic igniter cord system using an in-hole fuse, but this system results in a significant percentage of misfires and out-of- sequence blasts. Electrical initiation systems, on the other hand, are usually too costly to be commercially viable for large scale use.
It is accordingly an object of the invention to provide a method for the electrical sequential initiation of explosions which is relatively simple and which can be performed at relatively low cost.